We got them when DSs were 2 and 4 and they have been great. however, they are now 6 and 8 and I wouldn't buy them now. We are flying at Easter, and little one wants to take his....it will depend on baggage allowance whether he gets his wish.
Definitely wouldn't bother for a 6yo. My DS (age 4) has one that a friend gave us 2nd hand and I think it is pretty good as he generally pulls it behind himself and it does keep all his toys in one place for a journey. However I wouldn't buy one at full price - a pull along suitcase is probably more worthwhile. The main problem we've found with the Trunki is that it has to have a big space to open right up (something that zips is more useful as you can less obtrusively get things out/put things in).
agree they are one of those things that looks like it should be a really good idea but isnt. only ever see parents bent over pulling them. buy a fun coloured small suitcase with wheels. encourage your ds to put loads of stickers on it ( my girls put ribbons on theirs!) and then see how many he has after each journey etc. makes it much more fun especially for older kids
They are horrid, uncomfortable to carry when not on, don't fit under seat so up and down every 2 minutes getting something out of locker.
I would just give them a small rucksack with own things in. (2 and 3 year old here carry own snacks/ change of clothes and entertainment now- they also manage walk to and from plane so I would expect an almost 7 year old to tbh)